The present invention relates generally to the construction of sea defense systems in the open ocean, and more particularly to the construction of a man-made sea defense system using floatable caissons which are transported by floatation to a preselected ocean site and sunk in place to form the sea defense system.
Various methods have been developed for constructing artificial, man-made islands in the ocean. One method comprises the construction of steel and/or concrete platforms which stand on the ocean floor and the tops of which stand clear of the ocean surface. A major drawback of platform technology is that it is too expensive, in terms of construction and maintenance, to be used to construct large-scale artificial, man-made islands of any appreciable size. For example, it would not be economically feasible to use platform technology to construct an island large enough to provide even 100 acres of protected land or water, and it would be prohibitively expensive to construct such an island containing a thousand or more acres of protected land or water.
Another method is the construction of sea-walls by driving steel and/or concrete pilings deep into the ocean floor to form a containment structure which is then filled on the inside with dredged material. Using current sea-wall technology, it would not be economically feasible to construct a sea-wall capable of withstanding the extreme ocean environments of the open sea.
A widely used method is the construction of breakwaters, typically formed of rock, concrete blocks, concrete tetrapods and the like, which are filled on the inside with dredged material. Though breakwaters can be constructed to withstand even the most extreme ocean environments, they represent a large and permanent environmental "footprint.revreaction. on the ocean floor, especially if filled with dredged material.
Another method is the use of caissons, typically constructed of concrete and/or steel, which may be of either the floating or sunken type. A floating caisson floats on the ocean surface and is anchored to the ocean floor. A sunken caisson, on the other hand, rests directly on the ocean floor and may, depending on its construction, penetrate into the ocean floor to aid in anchoring the caisson in place. Floating caissons present a danger of breaking loose in severe wind and wave conditions, such as during a hurricane or typhoon, regardless of how strongly the caissons are anchored. This is an extremely dangerous condition and results in a breach of the sea defense system which, in turn, destroys the integrity of the protected area behind the caissons. Similarly, sunken caissons, even though large enough to rest on, or even penetrate, the ocean floor, also present a danger of breaking loose due to their hydrodynamic characteristics. For example, when severe storm waves and winds slam into the seaward side of a sunken caisson, the wind and wave forces create both a lifting force tending to lift the caisson off the ocean floor and a turning moment tending to turn the caisson--either of which if large enough in magnitude can lead to a caisson breaking loose thus resulting in a breach of the sea defense system.
Each of these methods of constructing artificial, man-made islands in the open ocean has one or more technical, economical and environmental problems associated with it. As a consequence, a few, if any, large-scale artificial, man-made islands have been built in the open ocean and, insofar as known to applicant, no such man-made islands have been built in open ocean waters in depths capable of taking all classes of sea-going vessels and subject to full force (hurricane and typhoon) waves and winds such as exist along, and off, the open coastlines surrounding the Atlantic, Pacific and Indian Oceans. Further complicating the problem of constructing artificial, man-made islands in the open ocean is the growing need to build any such complex so that, at least from an environmental or navigational standpoint, it can be de-mounted and removed following the end of its useful life thereby returning the ocean to, or as close as possible to, its pre-construction state.